Z-discs of abnormal appearance have been reported in skeletal muscle in a variety of myopathies. Alterations of heart muscle Z-disc structure have been reported in congestive heart failure, cardiac hypertrophy, in older hearts, and in the normal myocardium during growth periods. Tentomizing skeletal muscle also produced Z-lines of unusual appearance, similar or identical to those seen in the above conditions. The concept has recently evolved that the Z-line of muscle tissue in not simply an "inert" substance which serves to "anchor down" the thin filaments, but that it may serve as a template for formation of new muscle proteins in conditions of growth and repair. This interesting concept, however, lacks a sound experimental basis, and the significance of the presence of altered Z-structures in striated muscle remains obscure. We plan therefore to investigate morphological and chemical characteristics of Z-material in tenotomized soleus muscle of the rat. We will consider whether the various morphological types of Z-lines produced by tenotomy represent the same underlying process, and through antibody staining techniques, whether the rod bodies and streaming material are actually Z-protein. We will study the pattern of distribution of abnormal Z-lines, the influence of animal age on their production, their protein composition, and their ultrastructure. Through deafferentation of the soleus muscle, and cross nerve union experiments, we hope to gain information concerning the influence of the nervous system on the genesis of the abnormal Z-material. The research should yield structural and chemical information about the Z-discs of striated muscle, and give insight into the nature of the Z-alterations which occur in certain pathological conditions.